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PostPosted: Sun Apr 29, 2018 10:17 am 
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Joined: Mon Jun 30, 2008 2:16 pm
Posts: 356
Location: Ansonia, CT
I was still having an issue with loss of power and missing at high end revs (4-6K RPM). Since I replaced the points with a Pertronix unit, I thought it might be a fuel issue. So I replaced the fuel filter, which was overdue, then removed and dismantled both SU's. They weren't too dirty but I did notice a light brown coating in the bottom of the float bowels. This was easily removed with a good spray of carb cleaner.

After everything was cleaned up, I reassembled the SU's, backed off the idle (mixture) adjuster nut to the recommended 2-1/2 turns and installed the SU's. I hooked up the choke cables and throttle linkages and started her up. I then adjusted the idle stop screws, balanced the carbs and took her for a spin. The car ran well except the miss continued and high revs. :?

I am now convinced that the problem must still be a "timing" issue so I advanced the timing another 5 degrees or so and what do you know! Much better at high revs. The only problem I have now is that I get a bit of pinging at that high end under heavy acceleration, even though I am using 91 octane. I think today's gas formula is to blame! :evil: Any suggestions???

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1971 240Z original owner


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PostPosted: Sun Apr 29, 2018 11:30 am 
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Location: CT
I had similar problems all last year, also run pertronix, but I have a 10.25:1 CR.

I ran the highest octane fuel Sunoco offered but it still had the warning labels on it about the MethylEthylBadStuff they put into the fuel today. I got noticeable pinging until I put in some fuel octane enhancer, which raised my stumble/breakdown point by nearly 1,000 rpm. Vinny advanced the ignition and I got another 500 rpm out of the top end (up to 6000+). But my NGK sparkplugs were melting. They went pure white and the electrodes all turned to ashes and shrunk. I apparently used too much octane booster so I replaced the plugs and backed off on everything. I am told by friends I still have some pinging when I pass them AND the engine is prone to dieseling after shutdown, so my problems are still not solved. I can't reach 7,000 rpm in any gear and I refuse to try it in neutral without a load on the engine.
My cam comes on just at 3,400 and pulls hard all the way up thru 5500+, but soon after I begin to break down and stutter. I have replaced fuel pump, filter, plugs, and ensured the pertronix mechanically advances freely.

Everyone who passes me on the highway (in whatever car I am driving) smells bad. Not quite like a catalytic converter, but rancid fumes. I have to believe it's the cheap "EPA" fuel.

My own Z will climb that long Rte15-S hill in Woodbridge in 5th gear, maintaining 75mph without a stutter and accelerate if I ask it to, but it won't touch 7,000 anymore.

I also now have some mysterious 'missing coolant' issue which I haven't been able to trace completely. About a gallon of coolant suddenly disappeared from the radiator (but is not in the oil), resulting in rising engine temps. I am hoping it was just my radiator cap allowing it to blow-over, but the cap is reasonably new.

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PostPosted: Sun Apr 29, 2018 4:08 pm 
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Joined: Fri Dec 25, 2015 7:39 pm
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Location: Long Island, N.Y.
I am now convinced that the problem must still be a "timing" issue so I advanced the timing another 5 degrees or so and what do you know! Much better at high revs. The only problem I have now is that I get a bit of pinging at that high end under heavy acceleration, even though I am using 91 octane. I think today's gas formula is to blame! :evil: Any suggestions???[/quote]


I've experienced pinging, but usually under light acceleration, which meant it was running too lean to push the load until the pedal was gooZed to add more fuel. The fact that it's detonating under a firmer/richer condition suggests to me that you might want to check the resistance of wires to see if they meet the specifications of your pertronix ignition system ( which I have Zero knowledge of). The electrical system has to be balanced so that all components compliment each other (Thank you. You're welcome.) :lol: Too hot or weak of a coil, spark plugs that can't handle the spark or wires that can't handle the current might be causing the pinging and not allowing the higher revs that Frank mentions.

More fuel being dumped into an engine, for example, from larger carbs will not give more horsepower and performance unless the proper intake and exhaust manifolds (and air intake) capacities are proportionately increased. So maybe it's the plug wires? Would a hairline crack in the distributor cap cause arcing in the pertronix system? Maybe retarding the spark (duh!) one degree and giving each carb a 1/2 counter-clockwise turn for more fuel would help. :shock: It might be something very simple... like cleaning you grounds. :?: One never knowZ , do one? :mrgreen: Good luck.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor


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PostPosted: Mon Apr 30, 2018 4:58 pm 
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Joined: Mon Jun 30, 2008 2:16 pm
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Location: Ansonia, CT
The good input from both Frank and Howard is appreciated. :thumbs_up:

I have ruled out the distributor cap and rotor as it was also replaced. Also, this "miss" condition occurred even before I replaced the points with the Pertronix ignition system. The common denominator to me seems like its a timing/fuel grade issue. The car idles and runs very well, pulls hard even in high gear (low RPM) up hills without missing a beat. It's only when I really wind it out over 5K that I get that miss and loss of power.

Here's one other thought. :idea:
A couple of years ago I had questioned the forum on whether the standard distributor should have one or two springs on the mechanical advance. I questioned this after I had taken my distributor completely apart, only to find one of the "swing weights" was attached with a spring. I was expecting both weights to have them. The distributor was never opened up to this level before so if there were two springs, there should be one that let loose at the bottom of the distributor. But none was there. I have 3 different 240Z service manuals and none show any detail of the distributor weights.:roll:

I contacted our good friend Vinny Bedini and he told me that it should have two springs and gave me one from his vast inventory. This second spring has been installed for over a year now but it didn't effect the performance as far as I can tell. I can't help but think that there would be a difference in the advance curve with a one or two spring installation, with two springs possibly limiting the advance a little more, I think. :roll: I was wondering if anyone would have a timing curve for the 240Z including advance specs vs. revs which I could check out with my trusty Craftsman timing light. :wink:

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John Kish
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PostPosted: Mon Apr 30, 2018 8:03 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
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Location: CT
But you have a Pertronix now, right? So there's no vacuum advance? Would the curve chart be useful to you with those mods?

http://www.zcar.com/forum/10-70-83-tech ... curve.html

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1970 240Z


Last edited by Frank T on Mon Apr 30, 2018 8:16 pm, edited 1 time in total.

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PostPosted: Mon Apr 30, 2018 10:20 pm 
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Location: Ansonia, CT
Thanks Frank. I've read those forums already.

Yes, I have the Pertronix ignitor installed. But it only replaces the points so it still relies on the mechanical and vacuum advance.

I can't believe some of these other forum guys are running 30-37 degrees advance. I'd be pinging all the time with that much advance. Right now I think I've found the sweet spot where I have the advance set at around 8 degrees at idle with vacuum advance plugged. Some of these guys insist that it's just best to set the timing to where it starts to ping at load, then back it off a few degrees. Essentially that is what I've ended up with. I still think the new fuels have caused that timing setting "window" between good idle and high speed performance to narrow some. I had similar issues while recently trying to tune a 1973 TR6. These older cars lack the computers which on newer cars automatically adjust the timing, have knock sensors and constantly adjust fuel/air ratios when conditions change.

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John Kish
1971 240Z original owner


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PostPosted: Mon Apr 30, 2018 10:24 pm 
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Location: Somers CT
Sounds sensible to me that it would work that way. :thumbs_up: :thumbs_up:

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W.Karl Walton
Somers CT



75' - 280Z - HLS30203249 - #304 Gold Metallic (stockish)
96' - 300zx TT - JN1CZ24d3TX960293 - Black on Black (enhanced)


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PostPosted: Tue May 01, 2018 7:57 am 
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Location: CT
Yeah I run Pertronix too, but I remove and block the vac advance when checking/setting the timing. Vinny is racing at Road America this week but he said I wanted to start with 10*btdc when I find a working timing light. Mine is older than trees and nonfunctional and I haven't had time to replace it yet. Not sure why my car left his shop with more than that.

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PostPosted: Tue May 01, 2018 7:50 pm 
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Location: Ansonia, CT
Frank,
Bring it over to my place. We can time it here. I've got my car up on jack stands right now as I am doing some overdue brake maintenance. I recently bought new SS braided hoses and SS bridge lines and plan to bleed all four corners plus the clutch with fresh fluid. I'll be in my garage all day tomorrow.

Call me, you have my number. :wink:

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John Kish
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PostPosted: Tue May 01, 2018 8:22 pm 
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Thnx John, tmrw's already spoken for, and I dare not drive the Z that far until I time it and get a compression check, anyway. But I might be available to help bleed your brake lines later in the week?

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PostPosted: Wed May 02, 2018 7:40 pm 
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I held up replacing the brake hoses and bridge lines as I had some trouble with the first corner I tried. :thumbs_down: Using a tubing wrench, I couldn't get the brake line nut off which attaches the line from the car to the hose on the RF without destroying the nut and/or the line. The existing hoses and lines are in good shape anyway, so I just bled the master, all four corners and the clutch. All nice clean fluid, no air bubbles, thanks to my wife's help pumping the pedals. Stops on a dime. I also adjusted the rear brakes, cleaned the wheels inside and out and rotated them. I may try again replacing the hoses and bridge lines when I get younger. :wink:

Frank, the offer still stands, I can do the timing and the compression check at either your place or mine. Just say the word.

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PostPosted: Thu May 03, 2018 5:54 pm 
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I don’t know your engines hysteresis but, could be carbon build up, lower the dwell and plug gap keeping the timing at 32-35. Maybe even a cooler range plug. The only gas additives I use are stabil and mystery oil.

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PostPosted: Wed May 16, 2018 6:41 am 
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So you know, Octane is the ability to not burn, meaning more heat is required to burn 93 than it is to burn 89, meaning higher compression. Further more you should adjust the carbs with nothing hooked up to them first. Bottom knobs, for fuel, should start at 2 turns down, now adjust the top idle screws. You can use a rubber hose and listen to each throttle until they both have the same pitch. Car should idle very low, now turn up the fuel. Hopefully your valves are adjusted, your spark plugs are good and equally and correctly gaped. Make sure engine itself is correctly timed, then worry about ignition timing, and last, make sure the gap is set correctly on your pertronix system or it will not work correctly and make sure you use a good cap and rotor, like Nissan, Beck Arnly, Denso and both are from same company.


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PostPosted: Wed May 16, 2018 9:23 am 
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Thanks again for the inputs guys.

I'm sure it is a timing issue with my car. I've ruled out the fuel system as I've double and triple checked fuel supply, mixtures, octane, balancing the carbs, etc. I have also replaced the plug wires, distributor cap and rotor with new from Motorsport.

I'm still confused as to why my car is running better now with about 10 deg BTDC advance at idle (vacuum line plugged). When is set it back to factory setting of 5 degrees BTDC it bucks during acceleration.The Pertronix ignitor I installed has no adjustable gap setting as the module is fixed to a non adjustable back plate. I have the distributor advanced as much as I can without modifying the plate which has the securing adjustment bolt running though it.

My big question is why do I now need to run more advanced than I used to? I had always set the timing per the Datsun manuals at 5 degrees BTDC at idle before. :?

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PostPosted: Wed May 16, 2018 10:32 am 
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I don't have an answer for that, but invite you to consider that those manual specs were quoted from the old points-and-condenser ignition system. Pertronix gets installed in SO many different cars today I doubt they even issue specs for individual applications.

My L28 head is a highly modified E88 with 10.3:1 compression and big fat racing valves, a lumpy cam and titanium valve train. The 280 manuals tell me to use specific NGK spark plugs but because of all the mods I have made to the head and ignition, I've had to experiment with other heat ranges to find one which makes my engine happy.

Once you begin modifying things, factory tuning specs don't necessarily apply.

For awhile I was adding octane booster to my tank. That melted spark plugs and caused dieseling, which stopped when I returned to straight fuel.

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